The present invention relates to a sheet transportation control method according to which abnormal sheet transportation is detected based on the timing at which each one of sheet sensors disposed along a transportation path for transporting a sheet detects the sheet and based on a set time determined in advance, and upon detection of abnormal transportation, transportation of the sheet is stopped, and also to an image forming apparatus which controls, by such a sheet transportation control method, transportation of a sheet on which an image will be formed.
In an image forming apparatus such as a printer and a multi-function machine which prints (forms an image) on a paper (sheet), a jam (abnormal transportation) is detected based on intervals at which plural paper sensors disposed along a paper transportation path detect and based on a preset jam detection time (set time) determined in advance, and upon detection of a jam, the image forming apparatus stops operating, indicates the occurrence of the jam on a display panel or the like, and encourages a user to remove a jammed paper (See Japanese Patent Application Laid-Open No. 2002-160853 for instance.).
In these image forming apparatuses, multiple paper sensors are disposed at fixed locations which may be near a paper feeder roller, a registration roller and the like for example, a jam detection time, which is based on the inter-sensor distances, the paper transportation speed and chattering of the paper sensors, is calculated at the stage of designing or otherwise appropriate timing, and the calculated jam detection time is stored in a ROM (Read Only Memory) or the like in advance.
The jam detection time is set somewhat longer considering varying of the inter-sensor distances attributable to varied angles at which the paper sensors are disposed or uneven assembling of the transportation path, variations of the paper transportation speed caused by a varying paper feed/drive source, variations of a detection delay time due to differences between the individual paper sensors, etc., so as to obviate frequent jam detection.
However, as printing has become faster (from 40 sheets/second to 120 sheets/second for instance) over the recent years, in order to minimize the intervals of feeding papers (from 100 mm to 15 mm for example), it is difficult to set the jam detection time somewhat longer. High-speed printing therefore leads to a problem of frequent paper jam detection. Such rampant paper jam detection often includes erroneous detection by the paper sensors due to the varying paper transportation speed, etc. Frequent paper jam detection causes another problem that it is not possible to print at a high speed.